Laser Exposure System; Overview/Configuration; Overview; Controlling The Laser Activation Timing - Canon LBP2900 series Service Manual

2.3 LASER EXPOSURE SYSTEM

2.3.1 Overview/Configuration

2.3.1.1 Overview

The laser/scanner system serves to form images on the photosensitive drum according to the video signals coming from the video controller, and it consists
of a laser driver PCB, scanner motor, and the like, which are housed inside an assembly as a single unit. The laser/scanner system is controlled by the DC
controller.
The following is a diagram of the laser/scanner system and a description of its sequence of operation.
controller
1. When the print command arrives from the video controller, the engine controller turns on the scanner motor to rotate the 4-facet mirror.
2. When the scanner motor starts to rotate, the engine controller uses the laser control signal to force the laser on. Thereafter, the engine controller starts
to control the rotation of the scanner motor.
3. The engine controller uses the scanner motor speed control signal to make sure that the scanner motor rotates at a specific speed at all times.
4. When the scanner motor reaches a target rotation speed, the video controller sends video signals to the laser driver PCB.
5. The laser driver turns on the laser diode according to these signals.
6. The laser beam moves through a collimating lens and a cylindrical lens to reach the 4-facet mirror rotating at a specific speed.
7. The beam reflected by the 4-facet mirror then moves through the imaging lens and the reflecting mirror arranged in front of the 4-facet mirror and focus
on the surface of the photosensitive drum.
8. When the 4-facet mirror rotates at a specific speed, the laser beam starts to scan the surface of the photosensitive drum at a specific speed.
9. When the photosensitive drum rotates at a specific speed and, at the same time, the laser beam starts to scan the surface of the photosensitive drum at a
specific speed, a static (latent) image starts to form on the surface of the photosensitive drum.

2.3.2 Controlling the Laser Activation Timing

2.3.2.1 Turning On/Off the Laser

The machine controls the activation of the laser according to the laser control signals coming from the engine controller using the laser driver that turns on
and off the laser diode (LD). The following shows the circuit used to control the laser.
/BDI
VDO
/VDO
CNT0
CNT1
/BD
/ACC
/DEC
Video
Engine
controller
PCB PCB
Laser driver PCB
Cylindrical lens
BD
sensor
Four-sided Focusing lens
Scanner motor
mirror
F-2-2
Chapter 2
Photosensitive
drum
0008-0084
0008-0090
2-3